docs: Add Standard ML to community language extensions list (#55695)

Adds the Standard ML community extension
([omarjatoi/zed-sml](https://github.com/omarjatoi/zed-sml)) to
`docs/src/languages.md`. It is already published in the Zed extension
registry ([zed.dev/extensions/sml](https://zed.dev/extensions/sml)) and
provides Tree-sitter highlighting plus Millet LSP integration, but is
currently missing from the language documentation page.

Release Notes:

- N/A

docs/src/SUMMARY.md

@@ -139,6 +139,7 @@
 - [Scheme](./languages/scheme.md)
 - [Shell Script](./languages/sh.md)
 - [SQL](./languages/sql.md)
+- [Standard ML](./languages/sml.md)
 - [Svelte](./languages/svelte.md)
 - [Swift](./languages/swift.md)
 - [Tailwind CSS](./languages/tailwindcss.md)

docs/src/languages.md

@@ -66,6 +66,7 @@ Some work out-of-the box and others rely on 3rd party extensions.
 - [Scala](./languages/scala.md)
 - [Scheme](./languages/scheme.md)
 - [Shell Script](./languages/sh.md)
+- [Standard ML](./languages/sml.md)
 - [Svelte](./languages/svelte.md)
 - [Swift](./languages/swift.md)
 - [Tailwind CSS](./languages/tailwindcss.md) \*

docs/src/languages/sml.md

@@ -0,0 +1,28 @@
+---
+title: Standard ML
+description: "Configure Standard ML language support in Zed, including language servers, formatting, and debugging."
+---
+
+# Standard ML
+
+Standard ML support is available through the community-maintained [Standard ML extension](https://github.com/omarjatoi/zed-sml).
+
+- Tree-sitter: [MatthewFluet/tree-sitter-sml](https://github.com/MatthewFluet/tree-sitter-sml)
+- Language Server: [Millet](https://github.com/azdavis/millet)
+
+## Setup
+
+1. Install a Standard ML implementation such as [SML/NJ](https://www.smlnj.org/) or [MLton](http://mlton.org/) to compile and run your code.
+2. [Install Millet](https://github.com/azdavis/millet#install) and ensure `millet-ls` is on your `$PATH`.
+
+## Project setup
+
+For projects with more than one source file, Millet expects a single root group file. Create a `millet.toml` in the directory you open in Zed:
+
+```toml
+version = 1
+[workspace]
+root = "sources.mlb"
+```
+
+The root must be either a [ML Basis (MLB)](http://mlton.org/MLBasis) file (`.mlb`, used with MLton) or a [SML/NJ Compilation Manager (CM)](https://www.smlnj.org/doc/CM/new.pdf) file (`.cm`, used with SML/NJ). Files not transitively reachable from the root are not analyzed. See the [Millet manual](https://github.com/azdavis/millet/blob/main/docs/manual.md) for more options.